doc: admin-guide: remove explanation of "watchdog/%u"

"watchdog/%u" threads has be replaced by cpu_stop_work,
which will mislead the reader.
Signed-off-by: Wang Qing <wangqing@vivo.com>
Link: https://lore.kernel.org/r/1615801744-31548-1-git-send-email-wangqing@vivo.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/kernel-per-CPU-kthreads.rst

@@ -332,23 +332,3 @@ To reduce its OS jitter, do at least one of the following:
 	kthreads from being created in the first place.  However, please
 	note that this will not eliminate OS jitter, but will instead
 	shift it to RCU_SOFTIRQ.
-
-Name:
-  watchdog/%u
-
-Purpose:
-  Detect software lockups on each CPU.
-
-To reduce its OS jitter, do at least one of the following:
-
-1.	Build with CONFIG_LOCKUP_DETECTOR=n, which will prevent these
-	kthreads from being created in the first place.
-2.	Boot with "nosoftlockup=0", which will also prevent these kthreads
-	from being created.  Other related watchdog and softlockup boot
-	parameters may be found in Documentation/admin-guide/kernel-parameters.rst
-	and Documentation/watchdog/watchdog-parameters.rst.
-3.	Echo a zero to /proc/sys/kernel/watchdog to disable the
-	watchdog timer.
-4.	Echo a large number of /proc/sys/kernel/watchdog_thresh in
-	order to reduce the frequency of OS jitter due to the watchdog
-	timer down to a level that is acceptable for your workload.